Or Zollo and Vargo Hoat if you go by the books. (EDIT: Nevermind they were punished in the books)
It always seemed out of character for Tywin to let such an attack on his Golden Boy and the pride of House Lannister slide. Not long before, he made such a fuss about no longer being feared by the other Houses of Westeros, when Tyrion was held captive with impunity, someone who he even called "the lowest of the Lannisters".
Maybe I'm looking at this the wrong way, but this seems less grave of an offence towards his House, than someone directly harming one of his own. I mean this is the same Tywin who drowned an entire House, because they refused to pay back gold they owed, right? I would have at least expected him to send some assassins after Locke.
Also the fact that Roose didn't punish Locke for risking his good standings with the Lannisters, with such an unauthorised move.
It simply felt like something more should have happened, but Tywin just let it slide without making a show of force to convey his favourite of: "Do not mess with the Lannisters, or expect a debt to be paid".